Perspectives on the Neuroscience of Cognition and Consciousness

Spontaneous neuronal avalanches as a correlate of access consciousness

Decades of research have advanced our understanding of the biophysical mechanisms underlying consciousness. However, an overarching framework bridging between models of consciousness and the large-scale organization of spontaneous brain activity is still missing. Based on the observation that spontaneous brain activity dynamically switches between epochs of segregation and large-scale integration of information, we hypothesize a brain-state dependence of conscious access, whereby the presence of either segregated or integrated states marks distinct modes of information processing. We first review influential works on the neuronal correlates of consciousness, spontaneous resting-state brain activity and dynamical system theory. Then, we propose a test experiment to validate our hypothesis that conscious access occurs in aperiodic cycles, alternating windows where new incoming information is collected but not experienced, to punctuated short-lived integration events, where conscious access to previously collected content occurs. In particular, we suggest that the integration events correspond to neuronal avalanches, which are collective bursts of neuronal activity ubiquitously observed in electrophysiological recordings. If confirmed, the proposed framework would link the physics of spontaneous cortical dynamics, to the concept of ignition within the global neuronal workspace theory, whereby conscious access manifest itself as a burst of neuronal activity.

A Review of Theoretical Perspectives in Cognitive Science on the Presence of 1/f Scaling in Coordinated Physiological and Cognitive Processes

Time series of human performances present fluctuations around a mean value. These fluctuations are typically considered as insignificant, and attributable to random noise. Over recent decades, it became clear that temporal fluctuations possess interesting properties, however, one of which the property of fractal 1/f scaling. 1/f scaling indicates that a measured process extends over a wide range of timescales, suggesting an assembly over multiple scales simultaneously. This paper reviews neurological, physiological, and cognitive studies that corroborate the claim that 1/f scaling is most clearly present in healthy, well-coordinated activities. Prominent hypotheses about the origins of 1/f scaling are confronted with these reviewed studies. It is concluded that 1/f scaling in living systems appears to reflect their genuine complex nature, rather than constituting a coincidental side-effect. The consequences of fractal dynamics extending from the small spatial and temporal scales (e.g., neurons) to the larger scales of human behavior and cognition, are vast, and impact the way in which relevant research questions may be approached. Rather than focusing on specialized isolable subsystems, using additive linear methodologies, nonlinear dynamics, more elegantly so, imply a complex systems methodology, thereby exploiting, rather than rejecting, mathematical concepts that enable describing large sets of natural phenomena.

Three requirements for justifying an educational neuroscience

BACKGROUND

Over the past quarter century, efforts to bridge between research in the neurosciences and research, theory, and practice in education have grown from a mere hope to noteworthy scholarly sophistication. Many dedicated educational researchers have developed the secondary expertise in the necessary neurosciences and related fields to generate both empirical research and theoretical syntheses of noteworthy promise. Nonetheless, thoughtful and critical scholars in education have expressed concern about both the intellectual coherence and ethical dangers of this new area. It is still an open question whether educational neuroscience is for some time yet to remain only a formative study area for adventurous scholars or is already a fully fledged field of educational scholarship.

AIMS

In this paper, I suggest that to be a worthy field of educational research, educational neuroscience will need to address three issues: intellectual coherence, mutually informing and respected scholarly expertise, and an ethical commitment to the moral implications and obligations shared within educational research generally. I shall set forth some examples of lapses in this regard, focusing primarily on work on reading development, as that is my area of expertise, and make recommendations for due diligence. Arguments. First, intellectual coherence requires both precision in definition of technical terms (so that diverse scholars and professionals may communicate findings and insights consistently across fields), and precision in the logical warrants by which educational implications are drawn from empirical data from the neurosciences. Both needs are facilitated by careful attention to categorical boundary and avoidance of category error. Second, educational neuroscientists require focused and broad expertise in both the neurosciences and educational scholarship on teaching and learning in classrooms (and/or ancillary fields). If history is our guide, neuroscience implications for practice will prove unlikely in practice without expertise on practice. Additionally, respect for the expertise of others in this hybrid and necessarily collaborative enterprise is required. Third, educational neuroscience must take seriously the heightened moral and ethical concerns and commitments of educational professionals generally and educational researchers particularly. This means keeping a vigilant eye towards preserving the integrity of empirical and theoretical findings against rhetorical misuse by educational marketers, policy makers, and polemicists targeting the general public.

CONCLUSIONS

I conclude that educational neuroscience is more than a hybrid patchwork of individual interests constituting a study area, and is perhaps ready to stand as a legitimate field of educational inquiry. It will not be accepted as such, however, nor should it be, unless the need to demonstrate a capacity for consistent intellectual coherence, scholarly expertise, and ethical commitment is met.

Neuronal correlates to consciousness. The "Hall of Mirrors" metaphor describing consciousness as an epiphenomenon of multiple dynamic mosaics of cortical functional modules

Humans share the common intuition of a self that has access to an inner 'theater of mind' (Baars, 2003). The problem is how this internal theater is formed. Moving from Cook's view (Cook, 2008), we propose that the 'sentience' present in single excitable cells is integrated into units of neurons and glial cells transiently assembled into "functional modules" (FMs) organized as systems of encased networks (from cell networks to molecular networks). In line with Hebb's proposal of 'cell assemblies', FMs can be linked to form higher-order mosaics by means of reverberating circuits. Brain-level subjective awareness results from the binding phenomenon that coordinates several FM mosaics. Thus, consciousness may be thought as the global result of integrative processes taking place at different levels of miniaturization in plastic mosaics. On the basis of these neurobiological data and speculations and of the evidence of 'mirror neurons' the 'Hall of Mirrors' is proposed as a significant metaphor of consciousness. This article is part of a Special Issue entitled: Brain Integration.

Letting the brain speak for itself

Metaphors of Computation and Information tended to detract attention from the intrinsic modes of neural system functions, uncontaminated by the observer's role in collection, and interpretation of experimental data. Recognizing the self-referential mode of function, and the propensity for self-organization to critical states requires a fundamentally new orientation, based on Complex System Dynamics as non-ergodic, non-stationary processes with inverse-power-law statistical distributions. Accordingly, local cooperative processes, intrinsic to neural structures, and of fractal nature, call for applying Fractional Calculus and models of Random Walks with long-term memory in Theoretical Neuroscience studies.

Possible role of glia in cognitive impairment in schizophrenia

Cognitive impairment is a core disorder of the schizophrenia syndrome. Based on glial-neuronal interactions, a pathophysiological model is proposed that could be explanatory for cognitive impairment in schizophrenia. The model consists of three main hypotheses concerning the pathophysiology in tripartite synapses, oligodendrocyte-axonic interactions, and in the glial networks (astrocytic syncytium). In tripartite synapses nonfunctional astrocytic receptors may cause an unconstrained synaptic information flux, since they cannot be occupied by neurotransmitters (NTs). Therefore, a generalization of information processing may occur in the brain causing hallucinations, delusions, and thought disorder. If the oligodendrocyte-axonic system decomposes, the brain is unable to process information in qualitative domains or categories. This may lead to severe incoherence phenomena such as thought disorder. Supposing that in the astrocytic syncytium gap junctions (g.js) normally form plaques functioning as memory devices, loss of function of g.j. may also cause cognitive impairment, since the syncytium decomposes and g.j. plaques cannot be generated. These hypotheses are experimentally testable. Finally, the problem of treatment of patients with schizophrenia is discussed, in case the presented model of schizophrenia might be verified.

Possible effects of synaptic imbalances on oligodendrocyte-axonic interactions in schizophrenia: a hypothetical model

A model of glial-neuronal interactions is proposed that could be explanatory for the demyelination identified in brains with schizophrenia. It is based on two hypotheses: (1) that glia-neuron systems are functionally viable and important for normal brain function, and (2) that disruption of this postulated function disturbs the glial categorization function, as shown by formal analysis. According to this model, in schizophrenia receptors on astrocytes in glial-neuronal synaptic units are not functional, loosing their modulatory influence on synaptic neurotransmission. Hence, an unconstrained neurotransmission flux occurs that hyperactivates the axon and floods the cognate receptors of neurotransmitters on oligodendrocytes. The excess of neurotransmitters may have a toxic effect on oligodendrocytes and myelin, causing demyelination. In parallel, an increasing impairment of axons may disconnect neuronal networks. It is formally shown how oligodendrocytes normally categorize axonic information processing via their processes. Demyelination decomposes the oligodendrocyte-axonic system making it incapable to generate categories of information. This incoherence may be responsible for symptoms of disorganization in schizophrenia, such as thought disorder, inappropriate affect and incommunicable motor behavior. In parallel, the loss of oligodendrocytes affects gap junctions in the panglial syncytium, presumably responsible for memory impairment in schizophrenia.

Fractals in the nervous system: conceptual implications for theoretical neuroscience

This essay is presented with two principal objectives in mind: first, to document the prevalence of fractals at all levels of the nervous system, giving credence to the notion of their functional relevance; and second, to draw attention to the as yet still unresolved issues of the detailed relationships among power-law scaling, self-similarity, and self-organized criticality. As regards criticality, I will document that it has become a pivotal reference point in Neurodynamics. Furthermore, I will emphasize the not yet fully appreciated significance of allometric control processes. For dynamic fractals, I will assemble reasons for attributing to them the capacity to adapt task execution to contextual changes across a range of scales. The final Section consists of general reflections on the implications of the reviewed data, and identifies what appear to be issues of fundamental importance for future research in the rapidly evolving topic of this review.

Hypnotizability-related integration of perception and action

Hypnotizability is a cognitive trait able to modulate many behavioural/physiological processes and associated with peculiar functional characteristics of the frontal executive system. This review summarizes experimental results on hypnotizability-related differences in sensorimotor integration at a reflex and an integrated level (postural control) and suggests possible interpretations based on morpho-functional considerations. In particular, hypnotizability-related differences in spinal motoneurones excitability are described, and the role of attention and imagery in maintaining a stable upright stance when sensory information is reduced or altered and when attention is absorbed in cognitive tasks is discussed as a function of hypnotic susceptibility. The projections from prefrontal cortex to spinal motoneurones and the balance between the activation of the right and left cortical hemisphere are considered responsible for the hypnotizability-related modulation of reflex responses, while the differences in postural control between subjects with high (highs) and low (lows) hypnotic susceptibility are considered a possible consequence of the activity of the locus coeruleus, which is also involved in attention, and of the cerebellum, which might be responsible for different internal models of postural control. We suggest a highly pervasive role of hypnotic susceptibility in human behaviour through the modulation of the integration of perception and action, which could be relevant for neurorehabilitative treatments and for the adaptation to special environments.

Viewing brain processes as Critical State Transitions across levels of organization: Neural events in Cognition and Consciousness, and general principles

In this theoretical and speculative essay, I propose that insights into certain aspects of neural system functions can be gained from viewing brain function in terms of the branch of Statistical Mechanics currently referred to as "Modern Critical Theory" [Stanley, H.E., 1987. Introduction to Phase Transitions and Critical Phenomena. Oxford University Press; Marro, J., Dickman, R., 1999. Nonequilibrium Phase Transitions in Lattice Models. Cambridge University Press, Cambridge, UK]. The application of this framework is here explored in two stages: in the first place, its principles are applied to state transitions in global brain dynamics, with benchmarks of Cognitive Neuroscience providing the relevant empirical reference points. The second stage generalizes to suggest in more detail how the same principles could also apply to the relation between other levels of the structural-functional hierarchy of the nervous system and between neural assemblies. In this view, state transitions resulting from the processing at one level are the input to the next, in the image of a 'bucket brigade', with the content of each bucket being passed on along the chain, after having undergone a state transition. The unique features of a process of this kind will be discussed and illustrated.

Consciousness related neural events viewed as brain state space transitions

This theoretical and speculative essay addresses a categorical distinction between neural events of sensory-motor cognition and those presumably associated with consciousness. It proposes to view this distinction in the framework of the branch of Statistical Physics currently referred to as Modern Critical Theory (Stanley, Introduction to phase transitions and critical phenomena, 1987; Marro and Dickman, Nonequilibrium phase transitions in lattice, 1999). Based on established landmarks of brain dynamics, network configurations and their role for conveying oscillatory activity of certain frequencies bands, the question is examined: what kind of state space transitions can systems with these properties undergo, and could the relation between neural processes of sensory-motor cognition and those of events in consciousness be of the same category as is characterized by state transitions in non-equilibrium physical systems? Approaches for empirical validation of this view by suitably designed brain imaging studies, and for computational simulations of the proposed principle are discussed.

On the role of receptor–receptor interactions and volume transmission in learning and memory

Learning and memory seem to be inherent to a biological neural network. To emerge, they need an extensive functional connectivity, enabling a large repertoire of possible responses to stimuli, and sensitivity of the connectivity to activity, allowing for the selection of adaptive responses. According to the classical view about the organization of the CNS, the connectivity issue is realized by the huge amount of synaptic contacts each neuron establishes, while the adaptation of the network to specific tasks is obtained by mechanisms of activity-dependent synaptic plasticity. The discovery of direct receptor-receptor interactions at the level of the plasma membrane and the existence in the brain of two main modes of communication, the wiring transmission (such as the synaptic transmission) and the volume transmission (based on the diffusion of signals in the extracellular space), provided a broader view of the functional organization of the CNS with potential important consequences on the understanding of learning and memory processes. Owing to receptor-receptor interactions clusters of receptors, the receptor mosaics (RM), can be formed at the plasma membrane where they can work as collective functional units. As a consequence, the connections between the cells become themselves networks (molecular networks) able to adapt their function according to the stimuli they receive. Learning, therefore, can occur also at the level of RMs. Thus, memory formation seems not only to be a distributed process, but also to follow a hierarchical morpho-functional organization. Furthermore, the combination of the two different forms of transmission could allow processes of correlation and coordination to be established between networks and network elements without the need of additional physical connections, leading to a significant increase of the degrees of freedom available to the CNS for learning.

The incoherence hypothesis of schizophrenia: based on decomposed oligodendrocyte-axonic relations

Based on the findings of white matter abnormalities in brains with schizophrenia, it is hypothesized that this disorder may be responsible for symptoms of incoherence of schizophrenia. It is supposed that the processes of oligodendrocytes tie the various properties of axonic information conductance together into categories. For this oligodendrocytic computation capacity a formalism is proposed. In the case of a decrease or loss of oligodendroglia, a brain with schizophrenia is unable to categorize information processing, so that on a behavioral level symptoms of incoherence (thought disorder, etc.) occur. Similarities and differences in the pathophysiology of multiple sclerosis and schizophrenia are also shortly discussed. Together, a decomposition of the oligodendrocyte-axonic system may be responsible for symptoms of incoherence in schizophrenia.